Double Dianhydride Backbone Polyimide Aerogels with Enhanced Thermal Insulation for High‐Temperature Applications

Aerogels owe their high thermal insulation and other unique properties to their nanostructure configuration. However, controlling the aerogels' morphology is always a scientific challenge. In this study, double dianhydride backbone (double backbone) polyimide aerogels with tailored nanostructure assembly are created for the first time. This is achieved by controlled polymerization reaction of oligomers with distinct dianhydride monomers. Combining the two oligomers through a controlled polymerization reaction is a successful strategy for tailoring the aerogels nanostructure assembly as well as other properties. The fabricated double backbone aerogel presents 40% reduced thermal conductivity of 19.7 mW mK^?1 over previously studied polyimide aerogels along with the compression modulus of 1.64 MPa at a relatively low density of 0.068 g cm^?3. Such low thermal conductivity is comparable with the inorganic counterparts. Light in weight and high thermally insulated polyimide aerogels with suitable mechanical properties and high service temperature are an appropriate replacement for current fireproof insulation materials.     

煤矿区地面注浆多分支水平井装备及技术

地面注浆技术是煤矿水害防治的有效方法,注浆多分支水平井是地面注浆技术实施的基础。结合矿区地质条件、钻井工艺、注浆工艺等特点,优选注浆井施工用车载钻机、稀土永磁直驱泥浆泵、电磁波无线随钻测量系统、固控系统等装备,并对注浆井钻孔结构、轨迹控制、套管施工等关键技术进行研究。形成一套适用于注浆多分支水平井用钻井装备及关键技术,对煤矿水害防治工作具有重要意义。     

一种网间异常流量诊断处置方案

针对中国移动部分IDC客户违规转租带宽、发展第三方家宽、内容资源调度策略不合理而造成大量回源流量从CMNET骨干网出口疏通的网间异常流量行为,提出一种基于深度报文检测技术(DPI)技术的诊断处置方案。方案已成功应用于移动某省公司的IDC客户异常流量的诊断处置, IDC业务CMNET骨干网出口网间流量下降71.42%、减少经济损失,出口质量显著提高,异常流量行为显著减少、风险得以有效防控。     

An efficient algorithm for backbone construction in cognitive radio networks

Numerous research articles exist for backbone formation in wireless networks; however, they cannot be applied straightforward in cognitive radio network (CRN) due to its peculiar characteristics. Since virtual backbone has many advantages such as reduced routing overhead, dynamic maintenance, and fast convergence speed, we intend to propose a backbone formation protocol in CRN. In this paper, we propose a tree‐based backbone formation protocol along with its maintenance. Our protocol is based on non‐iterative approach, thus leading towards limited message overhead and faster convergence speed. The proposed algorithm first forms the tree by maintaining the parent‐child relationship, and second, the parent nodes are connected together to form the virtual backbone. In the end, we evaluate the performance our protocol through extensive simulations.     

面向主干网的网络级绿色节能机制

近些年,全球范围内的互联网高能耗问题引发了持续关注,节能已成为未来互联网研究的热门议题之一.面向主干网,提出一种网络级绿色节能机制：一方面,在全局视图中使用最小剩余容量优先的绿色路由算法规划全局路由路径,这样使得网络中开启的捆绑链路数目最小,从而实现第一步节能;另一方面,在局部视图中使用绿色降序最佳适应算法将流量负载汇聚到捆绑链路中的最小物理链路集合,这样可以尽可能多地关闭物理链路,从而实现进一步节能.提出的机制在节能的同时兼顾用户QoS需求的满足,在提供QoS保证的前提下最大化节能收益.为了全面评估该机制,选取3个典型主干网拓扑：CERNET2,GéANT和INTERNET2,分别在高负载、中负载和低负载的情形下,与其他3种节能机制从网络功耗和网络性能（平均路由跳数、物理链路关闭数目、路由成功率和运行时间）方面做详尽的对比分析.仿真结果表明：该机制节能效果显著,且有令人满意的性能表现.     

Naphthodithiophenediimide–Bithiopheneimide Copolymers for High-Performance n-Type Organic Thermoelectrics: Significant Impact of Backbone Orientation on Conductivity and Thermoelectric Performance

The development of n-type conjugated polymers with high electrical conductivity (σ) has continued to pose a massive challenge in organic thermoelectrics (OTEs). New structural insights into the charge-carrier transport are necessitated for the realization of high-performance OTEs. In this study, three new n-type copolymers, named pNB, pNB-Tz, and pNB-TzDP, consisting of naphthodithiophenediimide (NDTI) and bithiopheneimide (BTI) units, are synthesized by direct arylation polymerization. The backbone orientation is altered by incorporating thiazole units into the backbone and tuning the branching point of the side chain. The alteration of the backbone orientation from face-on to bimodal orientation with both face-on and edge-on fractions significantly impacts the σ and the power factors (PFs) of the polymers. As a result, pNB-TzDP, with the bimodal orientation, demonstrates a high σ of up to 11.6 S cm⁻¹ and PF of up to 53.4 µW m⁻¹ K⁻², which are among the highest in solution-processed n-doped conjugated polymers reported so far. Further studies reveal that the bimodal orientation of pNB-TzDP introduces 3D conduction channels and leads to better accommodation of dopants, which should be the key factors for the excellent thermoelectric performance.     

石墨热压还原Cu/Cu_(2)O金属陶瓷电导逾渗行为与微观结构分形表征EI北大核心CSCD

采用石墨热压还原法制备Cu/Cu_(2)O金属陶瓷复合材料,并测试不同导通相(Cu)体积含量Cu/Cu_(2)O金属陶瓷复合材料的直流电导率。为了实现对导通相形状、大小和分布状态的定量表征,通过对复合材料微观结构图像的二值化处理进行导通相分形维数计算,结合Cu/Cu_(2)O金属陶瓷复合材料的电逾渗行为,分析复合材料微观结构与电性能之间的对应关系。结果表明:随着导通相体积分数的增加,逾渗无限团簇和逾渗骨架的总量随之增大,但逾渗骨架密度在逾渗阈值附近波动。此外,Cu/Cu_(2)O金属陶瓷复合材料垂直热压方向与平行热压方向的分形维数相差约0.1。分形计算为定量表征导体/绝缘体双相复合材料中导通相的微观结构提供了一种计算方法,有助于对第二相随机分布的复合材料实现微观结构定量表征。     

半正弦循环交通动载下加筋砾性土动力特性研究

为研究交通荷载下加筋砾性土的动力特性,以土工格栅为加筋材料,开展了多级长期循环荷载下无筋、平铺、环形竖向及环形立体组合加筋等不同加筋形式的半正弦循环荷载下加筋饱和砾性土动三轴试验,同时也进行了半正弦循环荷载下土体阻尼比计算公式的推导,并研究了加筋层数和围压对环形立体组合加筋砾性土阻尼比、骨干曲线等动力特性的影响规律。试验结果表明:多级循环荷载下砾性土试样的阻尼比呈现前期增大随后减小的规律,阻尼比在动应变达到1%左右达到峰值,且加筋能够减小砾性土试样的阻尼比;Hardin-Drnevich模型适用于描述加筋砾性土的骨干曲线,且模型参数a、b与围压和加筋层数之间分别存在线性关系和指数关系,基于此提出适用于不同围压、不同加筋层数下环形立体组合加筋砾性土的骨干曲线方程。     

半正弦循环交通动载下加筋砾性土动力特性研究

为研究交通荷载下加筋砾性土的动力特性,以土工格栅为加筋材料,开展了多级长期循环荷载下无筋、平铺、环形竖向及环形立体组合加筋等不同加筋形式的半正弦循环荷载下加筋饱和砾性土动三轴试验,同时也进行了半正弦循环荷载下土体阻尼比计算公式的推导,并研究了加筋层数和围压对环形立体组合加筋砾性土阻尼比、骨干曲线等动力特性的影响规律。试验结果表明:多级循环荷载下砾性土试样的阻尼比呈现前期增大随后减小的规律,阻尼比在动应变达到1%左右达到峰值,且加筋能够减小砾性土试样的阻尼比;Hardin-Drnevich模型适用于描述加筋砾性土的骨干曲线,且模型参数a、b与围压和加筋层数之间分别存在线性关系和指数关系,基于此提出适用于不同围压、不同加筋层数下环形立体组合加筋砾性土的骨干曲线方程。     

基于改进Deeplab V3+网络的语义分割

深度学习的语义分割在计算机视觉领域中有非常广阔的发展前景,但许多分割效果较好网络模型占用内存大和处理单张图片耗时长.针对这个问题,把Deeplab V3+模型的骨干网（ResNet101）的瓶颈单元设计为1D非瓶颈单元,且对空洞空间金字塔池化模块（Atrous Spatial Pyramid Pooling,ASPP）的卷积层进行分解.该算法能大幅度降低Deeplab V3+网络的参数量,提高网络推理速度.基于PASCAL VOC 2012数据集进行对比实验,实验结果显示改进网络模型拥有更快的处理速度和更优的分割效果,且消耗更少的内存.